The Effects of Various Levels of Thiamine and Riboflavin Intake Upon the Utilization of Casein, Supplemented with Methionine

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Abstract
The effect of various levels of thiamine and riboflavin intake upon the utilization of casein, supplemented with methionine, was studied. The nitrogen balance technique with weanling rats was used in this investigation, following the general method of Mitchell. Necessary minor modifications in method did not affect the biological value of the test protein: (a) Utilization of the protein was similar when rats received dextrose in place of cornstarch as the source of carbohydrate; (b) depleting the rats of their major reserves of either thiamine or riboflavin did not permanently affect their ability to utilize the test protein when they were given the various vitamin supplements during the experimental period. The level of thiamine and riboflavin intake did not affect the digestibility of the protein. All digestibility values were between 97 and 100%. Statistical analysis of the data showed that the biological value of the test protein was significantly affected by the level of thiamine or riboflavin intake. Biological values for the test protein, obtained with the control groups of rats, were 89 and 95%. Rats receiving daily supplements of 1.25 and 2.50 µg of thiamine hydrochloride, with all other factors optimum, were unable to utilize the protein as efficiently as did those receiving the larger amounts, and biological values were significantly lowered to 53 and 76%, respectively. Rats receiving 5.0 µg of thiamine daily utilized their protein (biological value of 88%) as efficiently as did those receiving 10, 20 and 50 µg of the vitamin (biological values of 87, 95 and 90%). Groups of rats receiving daily supplements of 0, 1.25 and 2.50 µg of riboflavin did not utilize their protein as efficiently (biological values of 58, 81 and 81%) as did the control groups. At a 5.0 µg level of intake (biological value of 91%), protein utilization was as efficient as at the higher levels of 10, 20 and 50 µg of riboflavin (biological values of 87, 95 and 90%). Feeding supplements of both thiamine and riboflavin at a low level did not show an additive detrimental influence on the utilization of the protein.